Forces in alternating directions act on the conductor bars and coils (referred to for simplicity in the following text as windings, which are arranged in the slots in electrical machines) because of the interaction of the electric current flowing through the windings, and the magnetic field in the air gap. The windings should be held reliably in the slot even in the event of vibration and settling of the winding. It is therefore desirable for these windings to be held essentially without any play in the slots.
Various slot closure arrangements are known. By way of example, DE-A-2165727 proposes that a wave spring washer, which is in the form of a strip, be arranged between the sliding block and a pressure piece which protects the winding and is in the form of a strip. According to DE-A-2165727, the wave spring washer is essentially pressed flat for insertion, although the document does not mention the means by which this should be done.
EP-A-0601827 adopts a similar approach, and proposes that a wave spring washer in the form of a strip be arranged between the sliding block and a pressure piece which protects the winding and is in the form of a strip. In this case, the force used for attachment originates from the prestressing of the wave spring washer. In order to insert the slot closure arrangement into the slot, the wave spring washer is attached to the pressure piece in the prestressed state by a thermal adhesive (curing, fusing, activatable). After insertion, the adhesive joint is destroyed by heating, with the aim of recreating the spring effect.
Fundamentally CH-A-662911 proposes a similar design to the slot closure arrangement disclosed in DE-A-2165727. In a first embodiment, the wave spring washer is prestressed by adhesive bonding of the wave spring washer to the pressure piece and to the sliding block. In one alternative embodiment, the prestressing of the wave spring washer is produced via a screw connection which can be activated thermally and is subjected to a heat treatment after the positioning of the slot closure arrangement, with the aim of cancelling out the prestressing effect of the screw connection.
CH-A-525 581 proposes that the sliding block and the pressure piece each be designed to be conical in the longitudinal direction of the slot, thus creating a double inclined-wedge arrangement. The sliding block and the pressure piece are pressed against one another during assembly and/or subsequent stressing in the longitudinal direction of the slot.
EP-A-0639882, discloses a further option which proposes that the sliding block be designed in the form of laminates in the direction of the slot depth such that it acts as a spring element. In a similar manner to that in the case of CH-A-525 581, the sliding block and the pressure piece are once again in the form of a double inclined-wedge arrangement in the longitudinal direction of the slot.
A further solution approach is disclosed in the ABB international patent application published as WO 2008/141467, filed on May 18, 2007, and entitled “Method for securing winding bars in grooves of electric motors or generators.” The groove, or slot, closure arrangement has a spring element which is arranged between a pressure piece and a sliding block. During insertion of the slot closure arrangement into a slot, two leaf springs of the spring element, which are bent in the slot lateral direction, are adhesively bonded together using an adhesive which can be activated thermally. After the positioning of the slot closure arrangement in the slot, the adhesive joint is subjected to a heat source, to shock waves, to electromagnetic waves or to a chemical reaction, such that the adhesive joint is at least broken open, and the spring force of the spring element is recreated.
All of these slot closure arrangements have the common feature that the available spring movement distances are relatively short. These arrangements can involve complex production and complex insertion of the slot closure arrangement into the slot, and possibly undesirable adhesive residues. Practical use in the case of adhesive joints which can be activated thermally has shown that even similar adhesive joints which can be activated thermally often break open only at different temperatures and after different times of action. Because of the unpredictability of the slot closure arrangement in the assembled state, there can be a certain amount of uncertainty as to whether and to what extent the adhesive joint has actually broken open. The use of thermo-active screws or screws which can be activated thermally, can lose their strength after heating. In addition to the latent uncertainty relating to the quality of the bracing, broken-off screw residues can remain uncontrollably in the electrical machine.